1. Field of the Invention
This invention relates to a solid-state color image sensing device and more particularly to a solid-state color image sensing device which has a color mosaic filter adapted to correspond to each of the picture elements of a solid-state image sensing element.
2. Description of the Prior Art
Conventional solid-state color image sensing devices of this type employ a method of obtaining a primary color signal output from a multiplexed color signal from a plurality of picture elements, say, two picture elements. A conventional solid-state color image sensing device is provided with a color mosaic filter which is arranged, for example, as shown in FIG. 1 of the accompanying drawings, and is stuck to a frame transfer type CCD in such a way as to correspond to each picture element of the image pickup part thereof. Referring to FIG. 1, the mosaic filter includes green filter parts G, red filter parts R, blue filter parts B, magenta filter parts M (M=R+B) and light shielding parts X. The first row F1 of the filter parts consists entirely of the green filter parts G; the second row F2 consists of R, M, B and X repeatedly arranged; the third row F3 entirely consists of G; and the fourth row F4 consists of B, X, R and M repeatedly arranged. In this instance, the sum of the outputs of two picture elements in the first and second rows located in the same column in the vertical direction is taken as the output of one cell of a solid-state image sensing element (hereinafter called CCD) as shown in FIG. 2 and is read out one after another in the horizontal direction.
Accordingly, a color output signal is obtained through a zero horizontal scanning period OH of the CCD 1 as shown in FIG. 3(a). Output signals to be obtained through first and second horizontal scanning periods 1H and 2H are shown in FIGS. 3(b) and 3(c). In this instance, the signal of the CCD 1 is generally produced in the form of a pulse amplitude modulated (PAM) output. However, to facilitate understanding, only the signal portion of the output of the CCD 1 is taken into consideration herein.
The output of the CCD 1 is supplied directly to a subtractor 4 via signal line 1a and also to the subtractor 4 through a 1H delay line 3 which is arranged to delay the signal by one horizontal scanning period. With this arrangement employed, a color difference signal 2a of (0H-1H) and (1H-2H), i.e. a correlated signal relative to adjacent horizontal lines, is obtained at every horizontal scanning period as shown in FIGS. 4(a) and 4(b).
However, the color difference signal 2a has the polarity of its combination of R-B and M (or M and B-R) periodically inverted as shown in the drawing. To solve this problem, use of an inversion processing circuit 5 has been contemplated for carrying out an inversive process. A pulse oscillator 2 which produces an inversion control signal P1 is connected to the inversion processing circuit 5 as shown in FIGS. 4(c) and 4(d). With this arrangement used, an inversion control signal as shown in FIG. 4(c) is produced for (0H-1H) of the color difference signal 2a and another inversion control signal as shown in FIG 4(d) is produced for (1H-2H) of the color difference signal 2a. Then a color difference signal 3a which has the polarity made uniform for R-B and M is obtained at the output terminal 3a of the inversion processing circuit 5 as shown in FIG. 4(e). The color difference signal 3a then has its respective R-B and M portions sample held respectively by sample hold circuits 6 and 8 under the control of sample pulses SH1 and SH2 shown in FIGS. 4(f) and 4(g). This arrangement gives sample hold outputs 4a and 5a as shown in FIGS. 4(h) and 4(i). The signals 4a and 5a are guided to a low pass filters (LPF) 7 and 9 to remove unnecessary higher harmonic component. After that, color signals R and B are obtained through an adder 10 and a subtracter 11 which are arranged subsequent to the low pass filters 7 and 9.
This signal processing method, as described above, produces normal color signals by correcting the periodic polarities of the color difference signals determined by the color arrangement of the color mosaic filter. However, in inverting the polarity as described above, the (R-B) and M of the color difference signal are processed to be of inform polarity; then the signal is divided into color difference signals (R-B) and M; and then the color signals R and B are obtained through adding and subtracting operations. The conventional arrangement thus necessitates use of two channels of sample hold circuits. Further, since the signals to be handled are at least several MHz, it requires use of parts adapted for high speed operation. Besides, in accordance with the conventional method, much time is required for timing adjustment work on the sample hold circuits.